In video tape cartridges or audio tape cartridges of digital recording systems, there has been known to provide a braking mechanism for the tape hubs in video tape cartridges or audio tape cartridges using a digital recording system for preventing undesired rotation of the hubs when the tape cartridge is not in use.
One example of the braking mechanism for this purpose is disclosed in Japanese patent application Ser. No. 110274/1984 filed by the same applicant of this application. The tape cartridge disclosed in the patent application comprises a braking member having generally a gantry shape with a pair of legs formed on both ends of the braking member. The braking member is mounted in a case body so as to move back and forth with the braking member positioned at the front side of the hubs. The braking member is biassed in the back direction by a spring member (not shown) and when not in use, a pair of engaging bars which projected from the rear side of the braking member engage with engaging teeth formed on the outer peripheral of the top portion of the hubs for preventing rotation of the hubs. When the tape cartridge is mounted on a tape player, a releasing member of the tape player acts on the braking member directly or indirectly to move the braking member in the forward direction so that the engaging bars are disengaged from the engaging teeth to release the braking state of the hubs. Since the braking mechanism mentioned above can be applicable to such tape hubs without a flange portion i.e., flangeless hubs, it is advantageous to use the braking mechanism mentioned above when designing small sized tape cartridges.
In the tape cartridge using the braking mechanism mentioned above, the braking member is moved along the inner surface of the top wall of the tape cartridge rocking slightly in a vertical direction due to play between the top wall of the tape cartridge and the braking member. However, it is essential to prevent undesired contact of the braking member with the recording tape in the case body if the braking member is rocked during movement of the braking member. For this purpose, it has been attempted to lay a flexible slip sheet between the braking member and the top edge of the recording tape. In this case, however, since the slip sheet was supported by the braking member which was rocking vertically, the supporting surface of the slip sheet became unstable. For example, in the case where the braking member was moved in the forward direction, there occurred a stepped portion in the slip sheet corresponding to the rear end of the braking member, whereby the recording tape was wound irregularly, resulting in unstable tape running. As mentioned above, since the slip sheet is supported by the rocking braking member, there is the possibility of crushing the slip sheet which may cause a problem in running of the tape.
In place of using a flexible slip sheet, it has been suggested to dispose a rigid sheet made of a material such as vinyl chloride, below the inner face of a top wall of the case body, then inserting the braking member slidably in the gap between the top wall of the case body and the rigid sheet. However, this method requires attaching the rigid sheet below the inner face of the top wall one by one, therefore the amount of parts to be used and the number of work for assembling them are increased, thereby causing the production cost of the tape cartridge to be increased.